#include <bits/stdc++.h>
using namespace std ;

int N , M ;

struct _cos {
	int w ;
	int v ;
} a[3000010];

int f[3000100] ;


int main ( )
{
	f[1] = 1 ;
	cin >> N >>  M ;
	for ( int i = 1 ; i <= M ; i ++ ) {
		cin >> a[i].v ;
		cin >> a[i].w ;
	}
	
	for ( int i = 1 ; i <= M ; i ++ ) {
		for ( int j = N ; j >= a[i].v ; j -- ) {
			f[j] = max ( f[j] , f[j - a[i].v ] + a[i].v * a[i].w  ) ;
//			cout << f[j] << ' ';
		}
//		cout << endl ;
	}
	cout << f[N] ;
	return 0 ;
}